The invention relates to a device for filtering and separating fluids by pervaporation, microfiltration, ultrafiltration and reverse osmoses comprising a structure with an inlet opening for receiving the fluid to be separated and discharge openings for discharging the retentate and the permeate and including a plurality of disc-like spaced guide elements for guiding the fluid and a pocket-like filter element disposed between two adjacent guide elements and being exposed on both sides to the fluid flowing through the housing. The guide elements having passages formed at least at the edge areas thereof permitting passage of the fluid.
Such an apparatus is known from DE PS 39 15 197. Here, guide elements are used which have passages formed at opposite sides thereof to permit the fluid to be separated to pass or guide elements which have passages formed only at one side thereof. With this apparatus, a meander-like flow path can be established by the selective use of the guide elements with flow passages only at the apparatus ends or a parallel flow pattern can be established if the guide elements have the flow passages disposed all at the same end wherein the filter elements are disposed between the guide elements. In one case, the flow passages along the filter elements are arranged in series. In the other case, the flow passages are arranged in parallel-depending on the desired application.
The permeate passing into the filter element which has the form of a pocket membrane is discharged by way of a central opening formed in the filter element and is conducted out of the housing.
Pocket membranes are also called membrane pillows or pillow membranes; these expressions are synonymous.
In apparatus which utilize flat filter elements as in the present apparatus, it was found that zones are formed on the surface of the filter element which have different material transfer coefficients. This is caused by different flow conditions which are generated by particular design features of the apparatus. The main reason herefor is that, in order to obtain high pressure resistance and also for economical manufacturing reasons, such apparatus are generally circular and consequently the filter elements are also circular.
It has been observed that, in areas of the filter element with such structures with small material transfer coefficients expressed in Re (Reynolds) numbers, there is a small permeate flow in the areas with high Re numbers. The permeate flow does not increase at the same rate since, in these areas, the permeate flow approaches a limit value asymptotically. Basically, with the same entrance conditions for the medium to be separated in such an apparatus, for example, with regard to the fluid flow, the pressure, the temperature and the type of fluid, there should be the same Re number over the whole surface area of the filter element and, overall, there should be a higher permeate flow. It is noted however that the pressure loss increases exponentially in the areas with the increased Re numbers without resulting in an essentially increased permeate flow. The increased pressure loss particularly in the end areas of such an apparatus results in a reduced operating pressure and consequently in a reduction of the permeate flow.
Basically, this applies also to an apparatus as it is known from DE 37 15 183, wherein the fluid to be separated by the filter element which is enclosed between two flow guide members passes through the filter element from without to within and, in the subsequent filter element, from within to without and in the same way through the following filter elements.
It is the object of the present invention to provide a device for filtering and separating fluids wherein the fluid to be separated can flow over the whole effective area of the filter element with the same speed so that, with a constant flow channel width, also a uniform Re number is obtained for the total effective area of the filter element which provides for a uniform material transfer. Still zones in the area of the surfaces of the filter elements wherein high concentration of the material in the fluid could develop should not occur if the apparatus is operated according to the method of pervaporation which should be basically possible. The transport of large amounts of heat with the fluids to be separated to the location of separation within the apparatus should be possible so that a large temperature drop can be achieved over a short process distance. Also, the apparatus should be easy to manufacture and inexpensive to supply so that it can be used also for relatively low volume applications.